The field of this invention relates to a bearing assembly for the crank of a bicycle.
Bicycles, and particularly racing bicycles, must be manufactured with a high degree of precision and be accurately assembled and adjusted to insure optimum performance. Even slight power losses, due to friction caused by misalignment or improperly adjusted parts, are significant in view of the fact that all the power for operating the bicycle is derived from the rider. It is therefore important to eliminate sources of power loss, or at least reduce power loss so that the maximum amount of power will be derived to ride the bicycle.
In this regard, one particularly critical area is the pedal crankshaft which carries the chain sprocket and pedals. The crankshaft is supported within the hub by a bearing assembly. To insure most effective operation of the crank, there must be no "binding up" of the bearing assembly during rotation of the crank. Also, there must not be any slippage of the crank with respect to the bearing assembly and the total rotational movement of the crank is across the bearing assembly. Still further, the chain sprocket mounted on the crankshaft must be accurately aligned with the chain sprocket on the rear wheel of the bicycle. Any misalignment results in lost power.
It has been known that in order to obtain maximum power transmission, the hub casing must be manufactured to extremely close tolerances. These close tolerances are normally lost when the hub casing is welded to the frame of the bicycle due to thermal distortion during the welding operation. No matter how much care is taken in welding, it is virtually impossible to prevent thermal distortion from occurring. This thermal distortion causes the hub casing the assume other than a cylindrical configuration, with the configuration being a slight egg shape. The bearing assembly for the crank is designed to be installed within a cylindrical hub. When the installer attempts to insert the bearing assembly, the insertion becomes difficult, and in some cases, impossible to achieve. In the vast majority of the cases, the operator merely "hammers in" the bearing assembly in the position within the hub casing. As a result, the bearing assembly is initially stressed which causes such to either totally "bind up" and not operate, or operate at a less than maximum operating level.
In the past, attempts have been made to design a bearing assembly which compensates for the thermal distortion and slight difference of inside diameter and length of the hub casings. One common attempt relates to the use of bearing caps which are forced within each end of the hub casing. Although these bearing caps are allegedly designed to experience a minimal effect due to this distortion, such is normally not the case. Although the problem is diminished somewhat, still bearing assemblies are not able to freely rotate at the optimum level. Power losses and excessive wear does occur in operation of the crank within a prior art bicycle.